1. Field of the Invention
The present invention relates to a method for preparing a cellulose-based film based on pulp obtained by chemically treating wood and a cellulose-based film.
2. Description of the Prior Art
The increase of population, the development of various industries and the rapid development of the fast food industry have resulted in the phenomenon that disposable plastic packaging waste is generated in large quantities. Such plastic packaging waste semi-permanently maintains its original properties without being degraded, and thus interferes with the normal cycling of matter in the natural ecosystem and has a serious adverse effect on the living environment of people.
Thus, efforts have been made to reduce the amount of wasted plastic products through the promotion of plastic recycling, but these are not considered to be an ultimate method.
Biodegradable plastics receive attention along with the recycling of plastics. Although a standard world-wide definition for biodegradable plastics has not yet been established, biodegradable plastics can be defined as materials that have functions similar to those of general plastics in the use thereof and are biodegradable by microorganisms playing the most fundamental role in the cycling of matter in ecosystems.
Meanwhile, cellulose is the main component of higher plant cell walls and is a polysaccharide that makes up the majority of xylem. It is a straight-chain polymer of D-glucose units linked by β-1,4 bonds and represented by the chemical formula (C6H10O5)n. Also, it is an odorless, white solid and is insoluble in water. In addition, it has significantly strong resistance to alkali but is hydrolyzed by acid to glucose.
Cellulose is an organic compound next to coal in natural abundance and is considered to be an industrially very important resource. About 50% of wood and about 98% of cotton consist of cellulose. Cellulose is also found in bacteria, seaweed, and the shell of sea squirts, in addition to higher plants, and is also contained in an extracellular secretion of acetic acid bacteria. Furthermore, the sulfuric acid ester of cellulose is also present in the mucus of shellfishes. Cellulose is degraded by the cellulase of fungi bacteria, mollusks or the like, and then finally converted to glucose. Cellulose is a material having the highest molecular weight among polysaccharides, and the molecular weight thereof in the native state is in the range from a few tens of thousands to several hundreds of thousands.
An aggregation of a number of cellulose molecules forms fiber, and the minimum unit thereof is a micelle that is more than 0.05 nm in diameter and more than 0.6 nm in length. The results of X-ray analysis revealed that the micelle has a crystalline structure. The boundary between micelles is a non-crystalline region, and when cellulose fiber is immersed in water or dilute alkali it swells by absorbing the liquid, suggesting that the liquid infiltrates into the non-crystalline region. When cellulose fiber is immersed in concentrated alkali, the liquid infiltrates into the crystalline region. Cellulose has strong resistance to chemicals and is not invaded by microorganisms. In addition to being used as a raw material for producing paper and clothing, cellulose derivatives are used in various fields.
Among them, recycled cellulose, so-called cellophane, is an environment-friendly biodegradable packaging material, because it is based on pulp obtained by chemically treating wood. It has advantages in that it can be easily torn by hand, can be twisted and has no static electricity, such that dust does not adhere thereto. In addition, it shows excellent properties, including excellent transparency, gloss, heat resistance, oil resistance, chemical resistance and printability. A process for preparing a viscose solution and recycling cellulose has been used so far to process cellulose in the form of a film. However, such a viscose process causes serious pollution problems, that is, the environmentally harmful substance CS2 must be used in the preparation of the viscose solution, and the harmful substances CS2 and H2S are emitted during the recycling process. In addition, the viscose process is complicated, leading to the increase in production cost. Due to such problems, the use thereof is considerably decreasing.
The known applications of cellophane films include, in addition to general applications such as multicolor printing, lamination and twist packaging, various applications such as release films for fishing rods, flat panels and faced sheets, raw materials for cellophane tapes, packaging materials for processed meat products, overlapping films for cigarettes and cassette tapes, high moisture-proof films for soybean pastes, hard-boiled foods and drugs.
Currently, the demand for cellophane is decreasing due to the environmental harmfulness of a preparation process thereof and the high cost thereof. However, as the demand for biodegradable polymers has recently increased due to the launching of the Green Round in advanced countries and the construction of the ISO 14000 environmental management systems, cellophane is receiving attention again. Particularly, in order to fundamentally cope with international environmental regulations, including OECD restrictions on product process methods in OECD, restrictions on environmentally non-friendly products, and EU restrictions on electronic/electrical product waste disposal, all the processes of production must be converted to clean production systems.
In view of this fact, there is an urgent need to develop a method enabling the environmentally friendly production of a cellulose-based film advantageous in terms of environmentally friendly features.